Perforating gun assemblies are used in many oilfield and gas well completions. In particular, the assemblies may be used for, among other things, any or all of generating holes in downhole pipe/tubing (such as a steel casing) to gain access to an oil/gas deposit formation and to create flow paths for fluids used to clean and/or seal off a well, and perforating the oil/gas deposit formation to liberate the oil/gas from the formation. The perforating gun assemblies are usually cylindrical and include a detonating cord arranged within the interior of the assembly and connected to shaped charges, hollow charges or perforators disposed therein. Shaped charges are explosive components configured to focus ballistic energy onto a target. When the detonating cord initiates the explosive within the shaped charge, a liner and/or other materials within the shaped charge are collapsed and propelled out of the shaped charge in a perforating jet of thermal energy and solid material. The shaped charges may be designed such that the physical force, heat, and/or pressure of the perforating jet, expelled materials, and shaped charge explosion will perforate, among other things, steel, concrete, and geological formations.
Shaped charges for perforating guns used in wellbore operations come in many shapes/geometries. For example, shaped charges typically may be hemispherical, conical, frustoconical, or rectangular. The shape of the shaped charge in part determines the geometry of the perforating jet and/or perforation (hole) that is produced by the charge upon detonation. Hemispherical, conical, and frustoconical shaped charges (collectively, conical shaped charges or rotational symmetric shaped charges) tend to produce round/(semi-)circular perforations, while rectangular, or “slotted”, shaped charges tend to produce rectangular and/or linear perforations (“slots”). Particular geometries may be useful for specific applications in wellbore operations. For example, conical charges may produce a concentrated perforating jet that penetrates deep into a geological formation, to enhance access to oil/gas formations. Slotted shaped charges may produce linear perforations that can overlap each other in a helical pattern, and thereby perforate a cylindrical target around all 360° of the target. Such a pattern may be useful during abandonment of a well, where concrete is pumped into the well and must reach and seal substantially all areas of the wellbore.
One disadvantage of typical shaped charges is that the geometry of the shaped charge and associated perforating jet is set when the shaped charge is manufactured according to corresponding specifications. As such, a particularly-styled shaped charge must be kept on hand for each respective application in which a particular shaped charge is used. The limited, particularized use of different shaped charges thereby increases the costs and efforts associated with, e.g., manufacturing smaller batches of shaped charges, holding inventory of specific shaped charges, and transporting and keeping various styles of shaped charges at a job site.
Based at least on the above considerations, devices, systems, and methods for changing the perforation geometry of a shaped charge would provide economic and logistical benefits. For example, a standard charge may be adapted to produce a variety of perforation geometries, thus saving on manufacturing costs for customizing shaped charges and obviating the need to keep a variety of shaped charges at a wellbore location. These and other benefits are further served by devices, systems, and associated methods that are economical, adaptable to a variety of shaped charges and applications, and simple to execute.